docs: def all(pred: Callable, xs: Iterable):
      """
      Check whether all the elements of the iterable `xs`
      fullfill predicate `pred`.
  
      :param pred:
         predicate function
      :param xs:
         iterable object.
      :returns: boolean
      """
      for x in xs:
          if not pred(x):
              return False
  
      return True